Antioxidant activity of tocopherols,ascorbyl palmitate,and ascorbic acid and their mode of action

In the quest to use antioxidant compounds occurring in nature or related compounds, extensive studies have been made on vegetable oils, animal fats, apocarotenal, and vitamin A as substrates with ascorbyl palmitate, tocopherols, and ascorbic acid as antioxidants. Antioxidant efficiency varies with the substrate. Ascorbyl palmitate at a level of 0.01% provides a useful increase in the shelf-life of vegetable oils. Alone it is better than butylated hydroxytoluene and butylated hydroxyanisole and in combinations with other known antioxidants improves the shelf-life of all vegetable oils, as well as potato chips. Solubility problems with ascorbyl palmitate and other esters of ascorbic acid are discussed. The tocopherols have their greatest effect in protection of animal fats, carotenoids, and vitamin A. Experiments utilizing tocopherols and tocopherol combinations are presented. The activity of ascorbic acid, an excellent scavenger of oxygen, is reviewed. Quenchers of singlet oxygen do not inhibit the direct oxidation of fats and oils under the conditions used.     

Antioxidant activity and stability of 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid

6-Hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid in thin layer tests in vegetable oils and animal fats has two-four times the antioxidant activity of butylated hydroxytoluene and butylated hydroxyanisole and is more active than propyl gallate, nordihydroquaiaretic acid, ascorbyl palmitate, and α- and γ-tocopherols. It is also more active than tertiary butylhydroquinone in chicken and pork fats and corn, peanut, sunflower, and safflower oils in thin layer tests. Tertiary butylhydroquinone is slightly more active in corn, soybean, cottonseed, and peanut oils in the active oxygen method, probably due to decomposition of the chroman at 98 C. This decomposition is inhibited by ascorbic acid. The chroman is synergized by ascorbyl palmitate-thiodipropionate and ascorbic acids. Active oxygen method values of 190 hr are obtained in combination with the latter. A spectrofluorometric assay for 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid has been developed. The compound is 95–100% stable for 2 months at room temperature and 45 C, and a low level of toxicity is found. The copper and iron breakdown products of the chroman have been determined. A possible relationship between these products, protection of the chroman by ascorbic acid and ethylene diaminetetraacetic acid, and a mechanism of action is presented.     

The effect of primary antioxidants and synergists on the activity of plant extracts in lard

The antioxidant activities of combinations of plant extracts and primary antioxidants or citric acid were studied in lard stored at 75°C. Methanol extracts of oregano, thyme, marjoram, dittany, rosemary and sage were used. When combined with butylated hydroxyanisole, butylated hydroxytoluene or ascorbyl palmitate the extracts showed an additive antioxidant effect, while combinations with propyl gallate did not increase the induction period obtained by the phenolic antioxidant. Negative synergism was observed when the plant extracts were mixed with DL-α-tocopherol. Citric acid showed a high synergistic efficiency with marjoram extract and a minor one with thyme extract, but it had a negative effect with all the others. Ternary mixtures of the plant extracts with citric acid and ascorbyl palmitate had lower activity than the corresponding dual combinations with ascorbyl palmitate, except for the mixture of marjoram extract.     

Die Veränderungen von Nahrungsfetten bei höheren Temperaturen

Alterations of Edible Fats and Oils at Elevated Temperatures Refining of vegetable fats and oils has no deleterious effect upon their composition as far as desliming, neutralization or bleaching is concerned. However, during deodorization or physical refining small amounts of dimeric triglycerides and of trans fatty acids are formed depending on temperature and duration. The amounts of these by products are insignificant provided that the usual process conditions are applied. In the kitchen the various cooking methods can have quite different effects upon the quality of the fats and oils. Whereas boiling and baking have no effects and short-term shallow frying show only minor changes in quality, deep-fat frying can cause serious alterations especially if the oil is used far too long. Numerous investigations tried to identify these chemical reactions which are predominatly isomerizations as well as polymerization and oxidation reactions. The German Society for Fat Science and Federal Health Authorities in Germany issued recommendations for the assessment of fat deterioration basing on sensory evaluation in combination with some analytical data. Since 60 years and with considerable effort more or less systematic investigations have been performed to answer the question if heated fats are detrimental to human health. Fats and oils were heated under the conditions of good commercial practice and then fed to test animals. In some cases the heated fats were separated into various fractions and these were fed individually. The results of the most significant long-term feeding trials are reported and critically evaluated.     

Effects of tocopherols, ascorbyl palmitate, and lecithin on autoxidation of fish oil

The effects of α-, γ/δ, and δ-tocopherol concentrates (0.2–2.0%) alone and in combination with ascorbyl palmitate (0.1%) and lecithin (0.5%) on oxidative stability and flavor of fish oil were studied. Stability was assessed on oil stored in air at 20°C by peroxide value (PV) and off-flavor formation. Polymer content, para-anisidine value, and conjugation were used to characterize selected samples. When used alone, the protective effect of the tocopherols, as measured by PV, was δ≫γ/δ≫α, especially at the 2% concentration. Binary systems of ascorbyl palmitate-lecithin and lecithin-γ/δ or-δ-tocopherol were strongly synergistic in delaying peroxidation. The ternary blends provided the greatest protection against autoxidation. Refined fish oil with 2% δ-tocopherol, 0.1% ascorbyl palmitate, and 0.5% lecithin showed no significant peroxidation at 20°C over a period of 6 mon. The original antioxidant effect noted for the ternary systems in delaying peroxidation was not reflected in improved flavor stability. Off-flavors developed within 3 wk, making the oils unsuitable for use at high concentrations in ambient products that are unprotected from air.     

Biotechnology and oleochemicals: Changing patterns

Biotechnology will have a broad impact on the oleochemicals industry. Only a narrow range of this interface is discussed: (a) the use of organic solvents in the enzymatic synthesis of lipid derivatives, (b) the effect of the chemical nature of the feedstock on the production of microbial monoesters, and (c) temperature as a determinant of the level of unsaturation in biosynthetic lipids. Interest in running enzymatic reactions in high concentrations of organic solvents is increasing. The implications of such processes for the oleochemical industry is illustrated by examples of ester synthesis and interesterification of oils and fats. The dramatic effect of feedstock chemistry on the final monoester product mix produced byAcinetobacter sp. HO1-N is also discussed. Products resulting from usingn-alkanes (C₁₆−C₂₀), acetic and propionic acids and, most recently, ethanol and propanol, are illustrated. They range from a monoester mix resembling sperm oil to one similar to jojoba oil. In general, temperature inversely affects biolipid unsaturation: the low the temperature, the greater the unsaturation. The major function of this response is to preserve fluidity and function in biological membranes. The effect is universal in nature, occurring in animals, plants and microorganisms. Controlled laboratory studies have supported these observations made in nature. We have investigated the effect of temperature on the unsaturation of monoesters produced by the bacterium,Acimetobacter sp. HO1-N. The inverse relationship between temperature and unsaturation is clearly shown. The enzymatic basis for these results and the possibility of chemical or genetic modification of plants and microorganisms to produce more or less unsaturated lipids is briefly discussed. Organic solvents, feedstock chemistry and temperature stress in biocatalysis are but three of the variables at the interface of biotechnology and the oleochemicals industry that will cause changing patterns.     

Effects of Antioxidants on the Oxidative Stability of Oils Containing Arachidonic,Docosapentaenoic and Docosahexaenoic Acids

The effects of ascorbyl palmitate at 0, 300, 600, 900, or 1,200 ppm, tocopherol at 0, 200, 400, 600, or 800 ppm, and β-carotene at 0, 3, 6, 9, or 12 ppm on the oxidative stabilities of Oil 1, Oil 2, and Oil 3 containing 0, 0.55, and 0.67% of combined arachidonic acid (AA), docosapentaenoic acid (DPA), and docosahexaenoic acid (DHA), respectively, were studied by a central composite experimental design. The oxidative stability of oil was evaluated by determining the induction time using the Oxidative Stability Index. Ascorbyl palmitate and tocopherol had a significant effect on the stability of all three oils at α = 0.05. β-Carotene did not have any effect on the stability of oils at α = 0.05. The interaction effect of ascorbyl palmitate and tocopherol was significant for the three oils at α = 0.05. The induction time of oils decreased as the total amounts of AA, DPA and DHA increased from 0 to 0.55% or 0.55 to 0.67%. The addition of 1,200 ppm ascorbyl palmitate, 800 ppm tocopherol and 12 ppm β-carotene to Oils 1, 2, and 3 increased the induction time from 13.5 to 29.9 h, from 11.8 to 27.0 h, and from 10.5 to 20.0 h, respectively. The coefficient of determination (r ²) for the linear regression between the experimentally determined and statistically predicted induction time of the three oils was greater than 0.95. The use of an optimum combination of ascorbyl palmitate and tocopherols from the response surface analysis could improve the oxidative stabilities of oils containing AA, DPA and DHA.     

Use of cyclic anhydrides to remove cholesterol and other hydroxy compounds from fats and oils

A method for removing cholesterol from animal fats has been developed based on the reaction between the hydroxyl group of cholesterol and cyclic anhydrides. The reaction forms monoesters with acyl chains having a terminal free acid group. The conversion of cholesterol into an acid derivative makes it possible to remove the cholesterol from fats by extraction with aqueous alkali. A study of the reaction in model systems showed that optimal conditions were a molar ratio of cholesterol to succinic anhydride of 1∶3 at 135°C for several hours. Acid catalysts increased the rate of the reaction, and acetic was selected not only because of its catalytic power but also because its reflux prevented the distillation of the cyclic anhydride from the reaction mixture. If all the cyclic anhydride was added at the beginning of the reaction, animal fats such as lard, tallow and milk fats were reduced in their cholesterol content by about 40%. A study of the reaction mechanism showed that the cholesterol reduction could be increased to 60–70% by altering the amount and the addition sequence of cyclic anhydride. The effectiveness of acid catalysts was related inversely to the negative logarithm of their acid dissociation constant (pK), but as their effectiveness increased, so did their tendency to form other, unwanted esters of cholesterol. A mixture of monoethyl fumarate and acetic acid sped the reaction, compared with acetic acid alone, with minimal formation of cholesteryl acetate. Studies with¹⁴C-cholesterol showed little formation of products other than cholesteryl hemiscuccinate during the reaction. The procedure removed some of the tocopherol from the fat but had no other detectable effect on fat stability. The procedure also can be used to concentrate the lactone precursors from milk fat.     

Magnesium silicate treatment of dietary heated fats: Effects on rat liver enzyme activity

In an effort to reduce the deleterious nutritional effects of oxidation products generated in heated fats, a partially hydrogenated soybean oil (PHSBO) used 7 d (7-DH) for frying foodstuffs was obtained from a commercial deep-fat frying operation. The used fat was treated with magnesium silicate (T-7DH). Isocaloric diets containing 15% of either 7-DH or T-7-DH fats were prepared and fed to male weanling rats for 10 wk in a pair-feeding experiment and compared to control rats fed nonheated PHSBO (NH). Animals fed the 7-DH diet showed higher liver enzyme cytochrome b₅ and P₄₅₀ activity than the T-7DH diet compared to the NH group, suggesting a positive effect of the treatment. These results suggested the presence of lower amounts of harmful compounds in the diet containing the heated used oil which had been treated with the active adsorbent.     

The antioxidant properties of gallic acid and allied compounds

Summary The differences between animal fats and common vegetable oils as regards their protection by antioxidants are briefly reviewed; in general, the former can be stabilized by di- and poly-phenolic inhibitors and by inhibitols, the latter by acid-type inhibitors such as tartaric, phosphoric and other acids; these acids reinforce the action of the inhibitols which occur naturally in vegetable oils or which may be added to animal fats. A study has been made of the antioxygenic action of the polyphenols on both kinds of fats. The trihydric phenols, gallic acid and ethyl gallate are effective stabilizers in animal and vegetable fats and enhance the antioxygenic activity of inhibitols; they thus demonstrate the properties of both phenolic and acid inhibitors. The possible mechanism of this synergistic action is briefly discussed.     

Effects of selected chemical treatments on quality of fats used for deep frying

Maintaining quality of fats and oils used for deep frying is important in food preparation. In this study, commercially used shortenings were treated with various adsorbents and/or additives with a view to extending their useful life. Quality parameters monitored were increases in dielectric constant, free fatty acids, color (absorbance at 420 nm) and total polar materials. Bleaching clay, charcoal, magnesium oxide and Celite, and their mixtures, effectively reduced one or more of these parameters in used vegetable and animal-vegetable shortenings. However, when the treated fats were used to fry more french fried potatoes in the laboratory, they often deteriorated more rapidly than the untreated control fats. The daily addition of 200 ppm ascorbyl palmitate to fresh, partially hydrogenated soybean oil shortening used to fry french fries retarded free fatty acid development but increased color development and dielectric constant. Treatments employed to extend the useful life of frying fats improved quality parameters, but continued frying after treatment led to greater deterioration than occurred in the untreated control samples. Presented in part at the AOCS Annual Meeting in Philadelphia, PA in May, 1985.     

Why Concurrent CDDP and Radiotherapy Has Synergistic Antitumor Effects: A Review of In Vitro Experimental and Clinical-Based Studies

Chemo-radiotherapy, which combines chemotherapy with radiotherapy, has been clinically practiced since the 1970s, and various anticancer drugs have been shown to have a synergistic effect when used in combination with radiotherapy. In particular, cisplatin (CDDP), which is often the cornerstone of multi-drug combination cancer therapies, is highly versatile and frequently used in combination with radiotherapy for the treatment of many cancers. Therefore, the mechanisms underlying the synergistic effect of CDDP and radiotherapy have been widely investigated, although no definitive conclusions have been reached. We present a review of the combined use of CDDP and radiotherapy, including the latest findings, and propose a mechanism that could explain their synergistic effects. Our hypothesis involves the concepts of overlap and complementation. “Overlap” refers to the overlapping reactions of CDDP and radiation-induced excessive oxidative loading, which lead to accumulating damage to cell components, mostly within the cytoplasm. “Complementation” refers to the complementary functions of CDDP and radiation that lead to DNA damage, primarily in the nucleus. In fact, the two concepts are inseparable, but conceptualizing them separately will help us understand the mechanism underlying the synergism between radiation therapy and other anticancer drugs, and help us to design future radiosensitizers.     

Determination of milk fat in chocolates by gas-liquid chromatography of triglycerides and fatty acids

The combination of two routine methods is proposed to determine the content of milk fat (MF) in chocolates, which is applicable even in the presence of lauric fats or others. The content of MF is obtained from the sum of C₄₀, C₄₂, and C₄₄ medium-chain triglycerides, determined by capillary gas-liquid chromatography (GLC). A new method, based on methyl esters of lauric acid and on minor acids situated between myristic and palmitic, is proposed. It enables detection and estimation of potential lauric fats, as well as the determination of the actual content of MF. The influence of other vegetable and animal fats is discussed. We analyzed 45 MF samples extracted from industrial milk powders and from pure or fractionated MF for chocolate manufacturing or pastry by GLC of triglycerides. We also analyzed by capillary GLC the methyl esters from 22 of those fats. Mixtures of these 22 MF samples with a cocoa butter also were used for chromatographic analyses of methyl esters and triglyceride. Results from the various analytical methods have been presented.     

Relationship Between Physicochemical Properties and Moisture Barrier Property of Confectionery Coating Fats

Moisture migration in food causes deleterious effects on food quality such as loss of crispiness in ice cream cones, drying of chocolate with liquid centers, sugar bloom and cracking of compound/chocolate coating. The present study aimed to investigate the relationship between physicochemical properties of confectionery coating fats such as fatty acids and triacylglycerol (TAG) composition, solid fat contents, rheological and crystalline properties with their moisture barrier property. Coating fats with high content of trisaturated and desaturated TAG; and high SFC at 25 °C were found to have significant (P < 0.05) positive correlation with its moisture barrier property. These fats were able to crystallize into highly crystalline materials (high SFC) with small crystal size and dense networks. Thus, these fats were able to significantly delay moisture migration. Nevertheless, some of the highly crystalline fats also had high G′ value indicating poor mechanical properties and higher tendency of such fats to crack. In order to have good moisture barrier property, coating fats need to have sufficient solids with small crystal size and dense networks; and also low G′ value. Wafer coated with good moisture barrier fat showed less cracking during storage.     

Simultaneous determination of ascorbyl palmitate and nine phenolic antioxidants in vegetable oils and edible fats by HPLC

This study describes an HPLC method for the simultaneous determination of ascorbyl palmitate (AP) and synthetic phenolic antioxidants (SPA) in vegetable oils and edible fats in a single run. To achieve this, citric acid was used in combination with isoascorbic acid for stabilization of AP in standard and sample solutions and for deactivation of oxidizing agents in the HPLC system. SPA and AP were directly extracted from samples with methanol containing 1 mg/mL each of citric acid and isoascorbic acid. HPLC analytical and guard columns were pretreated with 90% methanol/acetonitrile 1∶1 (vol/vol), containing 4 mg/mL each of citric acid and isoascorbic acid, and 10% water at pH 3, for 30 min. Under these conditions, AP was stable for about 7 h at room temperature. The relative SD of repeatability for AP (0.5–3.6%) was comparable to that for SPA (0.3–2.8%). Average recovery from spiked samples was 100% for AP, 98–103% for SPA, and 85% for BHT (up to 90% using double extraction with methanol).     

Effects of antioxidants and humidity on the oxidative stability of microencapsulated fish oil

The effects of various antioxidants and RH on the oxidative stability of microencapsulated fish oil powder were investigated using PV and thiobarbituric acid tests. The micorencapsulation process provided high encapsulation efficiency (≥88% of extractable fish oil). Without antioxidants, the encapsulated fat was 10 times more stable against oxidation than the surface fat, as determined by PV. α-Tocopherol, which is a lipophilic antioxidant, showed a greater antioxidative effect in both surface and encapsulated fats than ascorbyl palmitate, which is an amphiphilic antioxidant. According to TBARS values, the longest lag period was observed at 0% RH. Addition of >200 ppm α-tocopherol in a 10–30% RH range prolonged the oxidative stability of the microencapsulated fish oil powder.     

Metal deactivation in lard

Summary A number of compounds, including known synergists, amino acids, and amines, have been evaluated as deactivators for copper, iron, nickel, and tin in lard. Some were effective in deactivating copper but were relatively poor for iron. One compound was better for iron than for copper. Ascorbyl palmitate, potassium ascorbyl palmitate, and ascorbic, tartaric, citric, and phosphoric acids were the most effective. This deactivation may in part explain the synergistic effect of these compounds with phenolic antioxidants. The more powerful antioxidants however are generally poor metal deactivators, and in the presence of traces of metallic pro-oxidants become relatively ineffective unless metal deactivators are also added. Presented at the Fall Meeting of the American Oil Chemists' Society, October 31–November 2, 1949. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U.S. Department of Agriculture.     

The speed of sound and isentropic bulk modulus of biodiesel at 21°C from atmospheric pressure to 35 MPa

Biodiesel, an alternative diesel fuel consisting of the alkyl monoesters of fatty acids from vegetable oils and animal fats, can be used in existing diesel engines without modification. However, property changes associated with the differences in chemical structure between biodiesel and petroleumbased diesel fuel may change the engine's injection timing. These injection timing changes can change the exhaust emissions and performance from the optimized settings chosen by the engine manufacturer. This study presents the results of measurements of the speed of sound and the isentropic bulk modulus for methyl and ethyl esters of fatty acids from soybean oil and compares them with No. 1 and No. 2 diesel fuel. Data are presented at 21±1°C and for pressures from atmospheric to 34.74 MPa. The results indicate that the speed of sound and bulk modulus of the monoesters of soybean oil are higher than those for diesel fuel and these can cause changes in the fuel injection timing of diesel engines. Linear equations were used to fit the data as a function of pressure, and the correlation constants are given.     

Oxidative Stability of Conventional and High-Oleic Vegetable Oils with Added Antioxidants

The oxidative stability of conventional and high-oleic varieties of commercial vegetable oils, with and without added antioxidants, was evaluated using the oil stability index (OSI). Oil varieties studied were soybean (SOY), partially-hydrogenated soybean (PHSOY), corn (CORN), sunflower (SUN), canola (CAN), high-oleic canola (HOCAN), very high-oleic canola (VHOCAN), oleic safflower (SAF) and high-oleic sunflower (HOSUN). One or more commercial antioxidants were added to the four most stable oils at supplier-recommended levels: rosemary extract (RM; 1,000 ppm), ascorbyl palmitate (AP; 1,000 ppm), tert-butylhydroquinone (TBHQ; 200 ppm), and mixed tocopherols (TOC; 200 ppm). OSI in hours (h) at 110 °C of the conventional oils were 5.2, 7.6, 8.4, 9.8, 10.9 and 14.3 h for SUN, SOY, CAN, CORN, PHSOY and SAF, respectively. OSI of high-oleic variants were 12.9, 16.5 and 18.5 h for HOCAN, HOSUN and VHOCAN, respectively. Maximum OSI values for the four most stable oils when treated with antioxidants, were 40.9, 48.5, 48.8 and 55.7 h for HOCAN, VHOCAN, SAF and HOSUN, respectively. Addition of TBHQ, alone and in combination with other antioxidants, resulted in the greatest increase in oxidative stability of SAF and other high-oleic oils evaluated. AP had a positive synergistic effect when used with TBHQ, while RM decreased TBHQ effectiveness.     

Antioxidative properties and enzymatic synthesis of ascorbyl FA esters

Efficient synthesis of unsaturated FA esters of ascorbic acid is possible with only a small excess of one of the reactants in t-amyl alcohol using Candida antarctica lipase as biocatalyst. Using free acids, we obtained yields that were comparable to yields reached using vinyl-activated acyl donors (71, 80, and 86% yields of esters with FA excesses of 1∶1, 1∶1.5, and 1∶2, respectively). As very low water activity is needed to achieve sufficiently high yields of product, molecular sieves were used to improve the ascorbyl ester yields. Ascorbyl oleate is more amorphous and has a much lower m.p. and lower enthalpy of fusion than ascorbyl palmitate. This leads to a higher solubility of ascorbyl oleate in oil, resulting in an increased antioxidant effect compared to that of the palmitate. In an accelerated storage test using deodorized rapeseed oil, samples incubated with ascorbyl palmitate showed noticeable oxidation after 1 wk of storage, whereas samples incubated with ascorbyl oleate displayed negligible oxidation for 9 and 4 wk at 30 and 40°C, respectively.